Chlorine
is a toxic, corrosive, greenish yellow gas with
a pungent, irritating odor. Chlorine belongs
to the halogen family of elements, found in
group VIIa of the periodic table. Chlorine is
produced mostly by electrolysis of brine; some
is obtained as a by-product in the manufacture
of sodium metal by the electrolysis of sodium
chloride either molten or in solution. Chlorine
is soluble in water. Its aqueous solution (
called chlorine water) consists of a mixture
of chlorine, hydrochloric acid, and hypochlorous
acid; only a part of the chlorine introduced
actually goes into solution, the major part
reacting chemically with the water. Chlorine
water has strong oxidizing properties resulting
from the oxygen set free when the unstable hypochlorous
acid decomposes. Chlorine combines directly
with almost all the elements except the rare
gases, excluding xenon, and nitrogen. Besides
the -1 oxidation state of the chlorides, chlorine
also exhibits oxidation state respectively :
+1 (hypochlorite, ClO- ), +3 (chlorite,
ClO-2), +5 (chlorate,
ClO-3 ) and +7 (perchlorate,
ClO-4). Very reactive
and unstable four oxide compounds have been
indirectly synthesized; chlorine monoxide (Cl2O),
chlorine dioxide (ClO2), dichlorine
hexoxide (Cl2O6), and
dichlorine heptoxide (Cl2O7).
Uncombined chlorine does not occur in nature
due to its activity, but its compounds are numerous.
Chlorine can displace the heavier halogens,
bromine and iodine, from their ionic compounds
and undergoes addition or substitution reactions
with organic compounds. Chlorine is used in
water purification; as a disinfectant and as
an antiseptic (mercuric chloride). Chlorine is a general biocide substance killing germs, micro-organisms, algae,
etc. The most widely used chloride chemical disinfectants are chlorine, ozone,
chlorine dioxide and chloramine.

Chloramine is an ammonium containing chlorine disinfectant. Monochloramine,
dichloramine and trichloramine are in equilibrium when produced by the chemical
chloramination of ammonia. Monochloramine is the only effective
ammonia-chloramine disinfectant. Dichloramine (NHCl2) and nitrogen trichloride
(NCl3) are too unstable to be useful and highly malodorous. Production
conditions are practically employed for the production of monochloramine by
lowering the pH and adjusting the molar ratios of the reactants. Chloramine is a
toxic yellow liquid at room temperature. Due to high CT values,
chloramine is a poor primary disinfectant but is an attractive secondary
disinfectant for the maintenance of a stable distribution system residual and
eliminating the formation of chlorination by-products. Chloramine is one of the most widely used chemical disinfectants in drinking
water system. Chloramine-B and
Chloramine-T are antiseptic agents derived from combining chloramine and
benzenesulfonamide (or p-toluenesulfonamide) repectively. Sulfonamide molecular
structure is similar to p-Aminobenzoic acid (PABA) which is needed in bacteria
organisms as a substrate of the enzyme dihydropteroate synthetase for the
synthesis of tetrahydrofolic acid (THF). Sulfonamides are capable of interfering
with the metabolic processes in bacteria that require PABA. They act as
antimicrobial agents by inhibiting bacterial growth and activity. Chloramine B
and Chloramine B are used as an oxidizing agent, an antiseptic, a germicide as
well as a chlorinating agent in organic synthesis. Its ions resulting from
dissolving in water involve in interfering with micro-organisms' cell process by
oxidations of proteins or enzyms.

Hypochlorite is an alternative choline source
when chlorine gas is impractical. The commercially available liquid hypochlorite
form is sodium hypochlorite (NaOCl) which is used as the disinfectant in
hospitals. But this is highly caustic, ethanol class disinfection has replaced.
Sodium hypochlorite have also been used extensively in the disinfection of
drinking-water. Hypochlorite anion,ClO-, changes the
oxidation-reduction potential of the cell, and resulting in the inactivations of
the micro-organism's function. Chlorine is used
to bleach fabrics, woodpulp and paper, to clean
dairy equipment, to control biofouling in cooling
systems, to shrink-proof wool, and to detin
and dezinc iron. Chlorine are used directly
or as an intermediate for the synthesis of many
organic chemicals; pesticides, antifreeze, refrigerants,
antiknock compounds, synthetic rubber and plastics,
chlorinated hydrocarbons, polyvinyl chloride,
ethylene dichloride hypochlorous acid, chlorobenzene,
chlorinated lime, carbon tetrachloride, ethylene
and propylene oxides, glycols, trichloroethylene,
perchloroethylene, chloroform, vinylidene chloride,
polychloroproprene, hydrogen chloride, metal
chlorides, chloracetic acid, chloral, synthetic
glycerine, methyl chlorides, chlorinated benzenes,
tetraethyl lead, fluorine compounds, titanium
tetrachloride, monochloroacetic acid, phosgene,
chloroisocyanuric acid, phosphorus chloride
dichlorobutene, and chlorinated paraffins.